/* This file is part of libDAI - http://www.libdai.org/
*
* libDAI is licensed under the terms of the GNU General Public License version
* 2, or (at your option) any later version. libDAI is distributed without any
* warranty. See the file COPYING for more details.
*
* Copyright (C) 2006-2010 Joris Mooij [joris dot mooij at libdai dot org]
* Copyright (C) 2006-2007 Radboud University Nijmegen, The Netherlands
*/
/// \file
/// \brief Defines the BipartiteGraph class, which represents a bipartite graph
#ifndef __defined_libdai_bipgraph_h
#define __defined_libdai_bipgraph_h
#include
#include
#include
#include
#include
namespace dai {
/// Represents the neighborhood structure of nodes in an undirected, bipartite graph.
/** A bipartite graph has two types of nodes: type 1 and type 2. Edges can occur only between
* nodes of different type. Nodes are indexed by an unsigned integer. If there are nrNodes1()
* nodes of type 1 and nrNodes2() nodes of type 2, the nodes of type 1 are numbered
* 0,1,2,...,nrNodes1()-1 and the nodes of type 2 are numbered 0,1,2,...,nrNodes2()-1. An edge
* between node \a n1 of type 1 and node \a n2 of type 2 is represented by a BipartiteGraph::Edge(\a n1,\a n2).
*
* A BipartiteGraph is implemented as a sparse adjacency list, i.e., it stores for each node a list of
* its neighboring nodes. More precisely: it stores for each node of type 1 a vector of Neighbor structures
* (accessible by the nb1() method) describing the neighboring nodes of type 2; similarly, for each node
* of type 2 it stores a vector of Neighbor structures (accessibly by the nb2() method) describing the
* neighboring nodes of type 1.
* Thus, each node has an associated variable of type BipartiteGraph::Neighbors, which is a vector of
* Neighbor structures, describing its neighboring nodes of the other type.
* \idea Cache second-order neighborhoods in BipartiteGraph.
*/
class BipartiteGraph {
public:
/// Describes the neighbor relationship of two nodes in a BipartiteGraph.
/** Sometimes we want to do an action, such as sending a
* message, for all edges in a graph. However, most graphs
* will be sparse, so we need some way of storing a set of
* the neighbors of a node, which is both fast and
* memory-efficient. We also need to be able to go between
* viewing node \a a as a neighbor of node \a b, and node \a b
* as a neighbor of node \a a. The Neighbor struct solves
* both of these problems. Each node has a list of neighbors,
* stored as a std::vector<\link Neighbor \endlink>, and
* extra information is included in the Neighbor struct which
* allows us to access a node as a neighbor of its neighbor
* (the \c dual member).
*
* By convention, variable identifiers naming indices into a
* vector of neighbors are prefixed with an underscore ("_").
* The neighbor list which they point into is then understood
* from context. For example:
*
* \code
* void BP::calcNewMessage( size_t i, size_t _I )
* \endcode
*
* Here, \a i is the "absolute" index of node i, but \a _I is
* understood as a "relative" index, giving node \a I 's entry in
* `nb1(i)`. The corresponding Neighbor structure can be
* accessed as `nb1(i,_I)` or `nb1(i)[_I]`. The
* absolute index of \a _I, which would be called \a I, can be
* recovered from the \c node member: `nb1(i,_I).node`.
* The \c iter member gives the relative index \a _I, and the
* \c dual member gives the "dual" relative index, i.e., the
* index of \a i in \a I 's neighbor list.
*
* \code
* Neighbor n = nb1(i,_I);
* n.node == I &&
* n.iter == _I &&
* nb2(n.node,n.dual).node == i
* \endcode
*
* In a FactorGraph, the nodes of type 1 represent variables, and
* the nodes of type 2 represent factors. For convenience, nb1() is
* called FactorGraph::nbV(), and nb2() is called FactorGraph::nbF().
*
* There is no easy way to transform a pair of absolute node
* indices \a i and \a I into a Neighbor structure relative
* to one of the nodes. Such a feature has never yet been
* found to be necessary. Iteration over edges can always be
* accomplished using the Neighbor lists, and by writing
* functions that accept relative indices:
* \code
* for( size_t i = 0; i < nrVars(); ++i )
* foreach( const Neighbor &I, nbV(i) )
* calcNewMessage( i, I.iter );
* \endcode
*/
struct Neighbor {
/// Corresponds to the index of this Neighbor entry in the vector of neighbors
size_t iter;
/// Contains the number of the neighboring node
size_t node;
/// Contains the "dual" iter
size_t dual;
/// Default constructor
Neighbor() {}
/// Constructor that sets the Neighbor members according to the parameters
Neighbor( size_t iter, size_t node, size_t dual ) : iter(iter), node(node), dual(dual) {}
/// Cast to \c size_t returns \c node member
operator size_t () const { return node; }
};
/// Describes the neighbors of some node.
typedef std::vector Neighbors;
/// Represents an edge: an Edge(\a n1,\a n2) corresponds to the edge between node \a n1 of type 1 and node \a n2 of type 2.
typedef std::pair Edge;
private:
/// Contains for each node of type 1 a vector of its neighbors
std::vector _nb1;
/// Contains for each node of type 2 a vector of its neighbors
std::vector _nb2;
/// Used internally by isTree()
struct levelType {
/// Indices of nodes of type 1
std::vector ind1;
/// Indices of nodes of type 2
std::vector ind2;
};
public:
/// \name Constructors and destructors
//@{
/// Default constructor (creates an empty bipartite graph)
BipartiteGraph() : _nb1(), _nb2() {}
/// Constructs BipartiteGraph from a range of edges.
/** \tparam EdgeInputIterator Iterator that iterates over instances of BipartiteGraph::Edge.
* \param nrNodes1 The number of nodes of type 1.
* \param nrNodes2 The number of nodes of type 2.
* \param begin Points to the first edge.
* \param end Points just beyond the last edge.
*/
template
BipartiteGraph( size_t nrNodes1, size_t nrNodes2, EdgeInputIterator begin, EdgeInputIterator end ) : _nb1(), _nb2() {
construct( nrNodes1, nrNodes2, begin, end );
}
//@}
/// \name Accessors and mutators
//@{
/// Returns constant reference to the \a _i2 'th neighbor of node \a i1 of type 1
const Neighbor & nb1( size_t i1, size_t _i2 ) const {
DAI_DEBASSERT( i1 < _nb1.size() );
DAI_DEBASSERT( _i2 < _nb1[i1].size() );
return _nb1[i1][_i2];
}
/// Returns reference to the \a _i2 'th neighbor of node \a i1 of type 1
Neighbor & nb1( size_t i1, size_t _i2 ) {
DAI_DEBASSERT( i1 < _nb1.size() );
DAI_DEBASSERT( _i2 < _nb1[i1].size() );
return _nb1[i1][_i2];
}
/// Returns constant reference to the \a _i1 'th neighbor of node \a i2 of type 2
const Neighbor & nb2( size_t i2, size_t _i1 ) const {
DAI_DEBASSERT( i2 < _nb2.size() );
DAI_DEBASSERT( _i1 < _nb2[i2].size() );
return _nb2[i2][_i1];
}
/// Returns reference to the \a _i1 'th neighbor of node \a i2 of type 2
Neighbor & nb2( size_t i2, size_t _i1 ) {
DAI_DEBASSERT( i2 < _nb2.size() );
DAI_DEBASSERT( _i1 < _nb2[i2].size() );
return _nb2[i2][_i1];
}
/// Returns constant reference to all neighbors of node \a i1 of type 1
const Neighbors & nb1( size_t i1 ) const {
DAI_DEBASSERT( i1 < _nb1.size() );
return _nb1[i1];
}
/// Returns reference to all neighbors of node \a i1 of type 1
Neighbors & nb1( size_t i1 ) {
DAI_DEBASSERT( i1 < _nb1.size() );
return _nb1[i1];
}
/// Returns constant reference to all neighbors of node \a i2 of type 2
const Neighbors & nb2( size_t i2 ) const {
DAI_DEBASSERT( i2 < _nb2.size() );
return _nb2[i2];
}
/// Returns reference to all neighbors of node \a i2 of type 2
Neighbors & nb2( size_t i2 ) {
DAI_DEBASSERT( i2 < _nb2.size() );
return _nb2[i2];
}
//@}
/// \name Adding nodes and edges
//@{
/// (Re)constructs BipartiteGraph from a range of edges.
/** \tparam EdgeInputIterator Iterator that iterates over instances of BipartiteGraph::Edge.
* \param nrNodes1 The number of nodes of type 1.
* \param nrNodes2 The number of nodes of type 2.
* \param begin Points to the first edge.
* \param end Points just beyond the last edge.
*/
template
void construct( size_t nrNodes1, size_t nrNodes2, EdgeInputIterator begin, EdgeInputIterator end );
/// Adds a node of type 1 without neighbors and returns the index of the added node.
size_t addNode1() { _nb1.push_back( Neighbors() ); return _nb1.size() - 1; }
/// Adds a node of type 2 without neighbors and returns the index of the added node.
size_t addNode2() { _nb2.push_back( Neighbors() ); return _nb2.size() - 1; }
/// Adds a node of type 1, with neighbors specified by a range of nodes of type 2.
/** \tparam NodeInputIterator Iterator that iterates over instances of \c size_t.
* \param begin Points to the first index of the nodes of type 2 that should become neighbors of the added node.
* \param end Points just beyond the last index of the nodes of type 2 that should become neighbors of the added node.
* \param sizeHint For improved efficiency, the size of the range may be specified by \a sizeHint.
* \returns Index of the added node.
*/
template
size_t addNode1( NodeInputIterator begin, NodeInputIterator end, size_t sizeHint = 0 ) {
Neighbors nbs1new;
nbs1new.reserve( sizeHint );
size_t iter = 0;
for( NodeInputIterator it = begin; it != end; ++it ) {
DAI_ASSERT( *it < nrNodes2() );
Neighbor nb1new( iter, *it, nb2(*it).size() );
Neighbor nb2new( nb2(*it).size(), nrNodes1(), iter++ );
nbs1new.push_back( nb1new );
nb2( *it ).push_back( nb2new );
}
_nb1.push_back( nbs1new );
return _nb1.size() - 1;
}
/// Adds a node of type 2, with neighbors specified by a range of nodes of type 1.
/** \tparam NodeInputIterator Iterator that iterates over instances of \c size_t.
* \param begin Points to the first index of the nodes of type 1 that should become neighbors of the added node.
* \param end Points just beyond the last index of the nodes of type 1 that should become neighbors of the added node.
* \param sizeHint For improved efficiency, the size of the range may be specified by \a sizeHint.
* \returns Index of the added node.
*/
template
size_t addNode2( NodeInputIterator begin, NodeInputIterator end, size_t sizeHint = 0 ) {
Neighbors nbs2new;
nbs2new.reserve( sizeHint );
size_t iter = 0;
for( NodeInputIterator it = begin; it != end; ++it ) {
DAI_ASSERT( *it < nrNodes1() );
Neighbor nb2new( iter, *it, nb1(*it).size() );
Neighbor nb1new( nb1(*it).size(), nrNodes2(), iter++ );
nbs2new.push_back( nb2new );
nb1( *it ).push_back( nb1new );
}
_nb2.push_back( nbs2new );
return _nb2.size() - 1;
}
/// Adds an edge between node \a n1 of type 1 and node \a n2 of type 2.
/** If \a check == \c true, only adds the edge if it does not exist already.
*/
void addEdge( size_t n1, size_t n2, bool check = true );
//@}
/// \name Erasing nodes and edges
//@{
/// Removes node \a n1 of type 1 and all incident edges; indices of other nodes are changed accordingly.
void eraseNode1( size_t n1 );
/// Removes node \a n2 of type 2 and all incident edges; indices of other nodes are changed accordingly.
void eraseNode2( size_t n2 );
/// Removes edge between node \a n1 of type 1 and node \a n2 of type 2.
void eraseEdge( size_t n1, size_t n2 );
//@}
/// \name Queries
//@{
/// Returns number of nodes of type 1
size_t nrNodes1() const { return _nb1.size(); }
/// Returns number of nodes of type 2
size_t nrNodes2() const { return _nb2.size(); }
/// Calculates the number of edges, time complexity: O(nrNodes1())
size_t nrEdges() const {
size_t sum = 0;
for( size_t i1 = 0; i1 < nrNodes1(); i1++ )
sum += nb1(i1).size();
return sum;
}
/// Calculates second-order neighbors (i.e., neighbors of neighbors) of node \a n1 of type 1.
/** If \a include == \c true, includes \a n1 itself, otherwise excludes \a n1.
*/
std::vector delta1( size_t n1, bool include = false ) const;
/// Calculates second-order neighbors (i.e., neighbors of neighbors) of node \a n2 of type 2.
/** If \a include == \c true, includes \a n2 itself, otherwise excludes \a n2.
*/
std::vector delta2( size_t n2, bool include = false ) const;
/// Returns true if the graph is connected
bool isConnected() const;
/// Returns true if the graph is a tree, i.e., if it is singly connected and connected.
bool isTree() const;
/// Asserts internal consistency
void checkConsistency() const;
//@}
/// \name Input and output
//@{
/// Writes this BipartiteGraph to an output stream in GraphViz .dot syntax
void printDot( std::ostream& os ) const;
//@}
};
template
void BipartiteGraph::construct( size_t nrNodes1, size_t nrNodes2, EdgeInputIterator begin, EdgeInputIterator end ) {
_nb1.clear();
_nb1.resize( nrNodes1 );
_nb2.clear();
_nb2.resize( nrNodes2 );
for( EdgeInputIterator e = begin; e != end; e++ ) {
#ifdef DAI_DEBUG
addEdge( e->first, e->second, true );
#else
addEdge( e->first, e->second, false );
#endif
}
}
} // end of namespace dai
/** \example example_bipgraph.cpp
* This example deals with the following bipartite graph:
* \dot
* graph example {
* ordering=out;
* subgraph cluster_type1 {
* node[shape=circle,width=0.4,fixedsize=true,style=filled];
* 12 [label="2"];
* 11 [label="1"];
* 10 [label="0"];
* }
* subgraph cluster_type2 {
* node[shape=polygon,regular=true,sides=4,width=0.4,fixedsize=true,style=filled];
* 21 [label="1"];
* 20 [label="0"];
* }
* 10 -- 20;
* 11 -- 20;
* 12 -- 20;
* 11 -- 21;
* 12 -- 21;
* }
* \enddot
* It has three nodes of type 1 (drawn as circles) and two nodes of type 2 (drawn as rectangles).
* Node 0 of type 1 has only one neighbor (node 0 of type 2), but node 0 of type 2 has three neighbors (nodes 0,1,2 of type 1).
* The example code shows how to construct a BipartiteGraph object representing this bipartite graph and
* how to iterate over nodes and their neighbors.
*
* \section Output
* \verbinclude examples/example_bipgraph.out
*
* \section Source
*/
#endif